Multicenter Ozone Study in oldEr Subjects (MOSES): Part 2. Effects of Personal and Ambient Concentrations of Ozone and Other Pollutants on Cardiovascular and Pulmonary Function.

INTRODUCTION

The Multicenter Ozone Study of oldEr Subjects (MOSES) was a multi-center study evaluating whether short-term controlled exposure of older, healthy individuals to low levels of ozone (O) induced acute changes in cardiovascular biomarkers. In MOSES Part 1 (MOSES 1), controlled O exposure caused concentration-related reductions in lung function with evidence of airway inflammation and injury, but without convincing evidence of effects on cardiovascular function. However, subjects' prior exposures to indoor and outdoor air pollution in the few hours and days before each MOSES controlled O exposure may have independently affected the study biomarkers and/or modified biomarker responses to the MOSES controlled O exposures.

METHODS

MOSES 1 was conducted at three clinical centers (University of California San Francisco, University of North Carolina, and University of Rochester Medical Center) and included healthy volunteers 55 to 70 years of age. Consented participants who successfully completed the screening and training sessions were enrolled in the study. All three clinical centers adhered to common standard operating procedures and used common tracking and data forms. Each subject was scheduled to participate in a total of 11 visits: screening visit, training visit, and three sets of exposure visits consisting of the pre-exposure day, the exposure day, and the post-exposure day. After completing the pre-exposure day, subjects spent the night in a nearby hotel. On exposure days, the subjects were exposed for 3 hours in random order to 0 ppb O (clean air), 70 ppb O, and 120 ppm O. During the exposure period the subjects alternated between 15 minutes of moderate exercise and 15 minutes of rest. A suite of cardiovascular and pulmonary endpoints was measured on the day before, the day of, and up to 22 hours after each exposure.

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In MOSES Part 2 (MOSES 2), we used a longitudinal panel study design, cardiopulmonary biomarker data from MOSES 1, passive cumulative personal exposure samples (PES) of O and nitrogen dioxide (NO) in the 72 hours before the pre-exposure visit, and hourly ambient air pollution and weather measurements in the 96 hours before the pre-exposure visit. We used mixed-effects linear regression and evaluated whether PES O and NO and these ambient pollutant concentrations in the 96 hours before the pre-exposure visit confounded the MOSES 1 controlled O exposure effects on the pre- to post-exposure biomarker changes (Aim 1), whether they modified these pre- to post-exposure biomarker responses to the controlled O exposures (Aim 2), whether they were associated with changes in biomarkers measured at the pre-exposure visit or morning of the exposure session (Aim 3), and whether they were associated with differences in the pre- to post-exposure biomarker changes independently of the controlled O exposures (Aim 4).

RESULTS

Ambient pollutant concentrations at each site were low and were regularly below the National Ambient Air Quality Standard levels. In Aim 1, the controlled O exposure effects on the pre- to post-exposure biomarker differences were little changed when PES or ambient pollutant concentrations in the previous 96 hours were included in the model, suggesting these were not confounders of the controlled O exposure/biomarker difference associations. In Aim 2, effects of MOSES controlled O exposures on forced expiratory volume in 1 second (FEV) and forced vital capacity (FVC) were modified by ambient NO and carbon monoxide (CO), and PES NO, with reductions in FEV and FVC observed only when these concentrations were "Medium" or "High" in the 72 hours before the pre-exposure visit. There was no such effect modification of the effect of controlled O exposure on any other cardiopulmonary biomarker.

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As hypothesized for Aim 3, increased ambient O concentrations were associated with decreased pre-exposure heart rate variability (HRV). For example, high frequency (HF) HRV decreased in association with increased ambient O concentrations in the 96 hours before the pre-exposure visit (-0.460 ln[ms]; 95% CI, -0.743 to -0.177 for each 10.35-ppb increase in O; = 0.002). However, in Aim 4 these increases in ambient O were also associated with increases in HF and low frequency (LF) HRV from pre- to post-exposure, likely reflecting a "recovery" of HRV during the MOSES O exposure sessions. Similar patterns across Aims 3 and 4 were observed for LF (the other primary HRV marker), and standard deviation of normal-to-normal sinus beat intervals (SDNN) and root mean square of successive differences in normal-to-normal sinus beat intervals (RMSSD) (secondary HRV markers).

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Similar Aim 3 and Aim 4 patterns were observed for FEV and FVC in association with increases in ambient PM with an aerodynamic diameter ≤ 2.5 μm (PM), CO, and NO in the 96 hours before the pre-exposure visit. For Aim 3, small decreases in pre-exposure FEV were significantly associated with interquartile range (IQR) increases in PM concentrations in the 1 hour before the pre-exposure visit (-0.022 L; 95% CI, -0.037 to -0.006; = 0.007), CO in the 3 hours before the pre-exposure visit (-0.046 L; 95% CI, -0.076 to -0.016; = 0.003), and NO in the 72 hours before the pre-exposure visit (-0.030 L; 95% CI, -0.052 to -0.008; = 0.007). However, FEV was not associated with ambient O or sulfur dioxide (SO), or PES O or NO (Aim 3). For Aim 4, increased FEV across the exposure session (post-exposure minus pre-exposure) was marginally significantly associated with each 4.1-ppb increase in PES O concentration (0.010 L; 95% CI, 0.004 to 0.026; = 0.010), as well as ambient PM and CO at all lag times. FVC showed similar associations, with patterns of decreased pre-exposure FVC associated with increased PM, CO, and NO at most lag times, and increased FVC across the exposure session also associated with increased concentrations of the same pollutants, reflecting a similar recovery. However, increased pollutant concentrations were not associated with adverse changes in pre-exposure levels or pre- to post-exposure changes in biomarkers of cardiac repolarization, ST segment, vascular function, nitrotyrosine as a measure of oxidative stress, prothrombotic state, systemic inflammation, lung injury, or sputum polymorphonuclear leukocyte (PMN) percentage as a measure of airway inflammation.

CONCLUSIONS

Our previous MOSES 1 findings of controlled O exposure effects on pulmonary function, but not on any cardiovascular biomarker, were not confounded by ambient or personal O or other pollutant exposures in the 96 and 72 hours before the pre-exposure visit. Further, these MOSES 1 O effects were generally not modified, blunted, or lessened by these same ambient and personal pollutant exposures. However, the reductions in markers of pulmonary function by the MOSES 1 controlled O exposure were modified by ambient NO and CO, and PES NO, with reductions observed only when these pollutant concentrations were elevated in the few hours and days before the pre-exposure visit. Increased ambient O concentrations were associated with reduced HRV, with "recovery" during exposure visits. Increased ambient PM, NO, and CO were associated with reduced pulmonary function, independent of the MOSES-controlled O exposures. Increased pollutant concentrations were not associated with pre-exposure or pre- to post-exposure changes in other cardiopulmonary biomarkers. Future controlled exposure studies should consider the effect of ambient pollutants on pre-exposure biomarker levels and whether ambient pollutants modify any health response to a controlled pollutant exposure.